ABSTRACT
True Triaxial Unloading (TTU) strength has utmost importance to study the actual behavior of intact rocks upon excavation as compared to traditional triaxial tests. It can be used to understand the mechanisms behind spalling and rockburst in construction of underground structures. The objective of the article is to derive unloading strength envelopes of different kinds of Indian rocks by unloading the minor principal stress (σ3), keeping the intermediate stress (σ2) constant from triaxial loading condition till failure and its influence on rockburst potential using poly axial strength testing machine at Rock Laboratory IIT, Delhi. Three different kind of rocks i.e, Jalore granite (Igneous), Makrana marble (Metamorphic) and Jodhpur sandstone (Sedimentary) were selected and tested for their triaxial loading and unloading strength envelopes in the laboratory to study the behavior of rocks under poly axial confinements. This research shows that the area between the true triaxial loading and unloading strength envelopes depict the zone of confinement in which rockburst will be observed. The results indicate that the potential of the rocks for strainburst increases with increase in separation of the failure envelopes mentioned above.
